C4stro the x800 xl just dropped to $270, pretty sweet deal...
So that's like a $90 difference now. But do you realize that the x800 xl, if you spend the extra $90, is actually a better deal? It is a lot more powerful than the 6600 gt. Let me give you some quick stats comparison.
X800 XL
Memory Bus Width: 256bit
Memory: 256MB GDDR3
Pixel Pipelines: 16
Vertex Pipelines: 6
Core Clock: 400MHZ
Memory Clock: 980MHZ
RAMDAC: 400MHZ
3D Support: DirectX 9, OpenGL 2.0
Pixel Shader Profile: 2.0B
Fill Rate: 6.4 Billion texels/s
Memory Bandwidth: 31.36 GB/s
6600 GT
Memory Bus Width: 128bit
Memory: 128MB GDDR3
Pixel Pipelines: 8
Vertex Pipelines: 3
Core Clock: 500MHZ
Memory Clock: 1000MHZ
RAMDAC: 400MHZ
3D Support: DirectX 9, OpenGL 1.5
Pixel Shader Profile: 3.0
Fill Rate: 4.0 Billion texels/s
Memory Bandwidth: 16 GB/s
AS you can see it is a much more powerful card, especially in the memory department. Of course if also depends on the game, but in general the x800 xl is a very powerful high-end card while the 6600 gt is a weaker budget card.
If you don't plan on upgrading soon I would try to budget in the x800 xl, heck dropa hard drive if you need to. The video card is more important.